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Thermal stratification which is common in water bodies is subject to such factors as the water depth of the water body (a lake or reservoir, for instance), the fluidity of the water and the local meteorological conditions. The stable thermal stratification in reservoirs will lead to changes in the physical and chemical properties of the water as well as distribution of aquatic creatures, hence leaving an impact on the water quality. The Daheiting Reservoir was taken as the research object in this study. Based on the continuous monitored water temperature data in the reservoir, the tempo-spatial change features of the water temperature structure in the reservoir were analyzed, and the driving factors of thermal stratification in the reservoir was studied. The research found that air temperature, wind speed, and hydrodynamic factors are the driving factors for the thermal stratification and corresponding water temperature change patterns in Daheiting Reservoir. Among these factors, air temperature is the fundamental precondition, the wind speed is the auxiliary precondition, and the hydrodynamic factors are the disturbance factors for thermal stratification in the Reservoir. All these factors act together to cause the thermal stratification pattern and evolution features in Daheiting Reservoir.

The composition and seasonal variation of the phytoplankton and bacterioplankton community were investigated, and SPSS and redundancy analysis (RDA) were used to explore the relationship between the phytoplankton and bacterioplankton community dynamics in the typical plateau Lake of Lake Erhai from July 2009 to April 2010. Obvious seasonal variation of phytoplankton was observed, and the abundance of phytoplankton ranged from 2.02 × 106 to 57.9 × 106 cells/L. The dominant species in autumn and summer was Microcystis sp., Psephonema aenigmaticum Skuja was dominant in winter, and Microcystis sp., Aphanizonmenon flos-aquae, Asterionella sp., P. aenigmaticum, etc. were dominant in spring. The abundance of bacterioplankton in the whole lake changed between 1.93 × 109 and 4.61 × 109 cells/L showing distinct seasonal variation characteristics. The results of correlation and RDA indicated that the abundance and community diversity of bacterioplankton were significantly correlated with the abundance of phytoplankton, and the group of Bacteroidetes had obvious correlation with Microcystis sp. and other cyanobacteria, which might have some links with the harmful algal blooms in Lake Erhai. Further research is needed to study the mechanisms of interactions between phytoplankton and bacterioplankton communities.

Three Gorges Reservoir(TGR) is a giant canyon-shaped reservoir located in the lower section of the upper reaches of the Yangtze River.After impoundment,hydrological signatures,chemical factors and species composition,had been greatly changed in TGR.The new environmental conditions could increase methylmercury(MeHg) production,and induce substantial increase of mercury concentration in the predator fish through food chain biomagnification.Concern about human consumption of fish contaminated with MeHg had been raised even before the construction of TGR.This study tried to investigate the total mercury concentrations in fish and biomagnification characters of mercury along food chains in TGR after 175m impoundment.The stable isotope analysis could be a useful method of checking and evaluating the trophic conditions of aquatic ecology.We collected eleven fish species from three main stem sections and seven typical tributaries of TGR from 2011 to 2012.Carp(Cyprinus carpio) was selected as a typical species to investigate the spatial distribution of mercury level in fish from TGR.Total mercury concentrations and stable isotope ratios(δ13C and δ15N) of all fish samples were determined.Result showed that mercury concentrations in fishes from TGR had not obviously increased after impoundment.The carp mercury concentrations in TGR were comparable to values reported for other areas of Yangtze River Basin.But spatial difference was found among different sections of main stem.Due to the enhanced sediment deposition along reservoir,there was a decreasing trend of mercury concentration in fish from upper stream to lower stream within TGR.Mercury concentrations in the fishes from Luoqi in up area of reservoir(88.0μg/kg,average) was significantly higher than those from Wushan in middle area of reservoir(43.1μg/kg,average) and tributaries(57.1μg/kg,average).The mercury concentrations in fish from tributaries were comparable to those from main stem,and there were no significant difference among most tributaries.Based on the carbon and nitrogen stable isotope ratios and total mercury contents in eleven species fish,the biomagnification power of mercury in two sections and one tributary were evaluated.While log-transformed mercury contents were consistently correlated with δ15N values for the fish food web in all sampling sites,the slope of the relationship with δ15N(biomagnification power value) was significant higher in Shennong River than that in Wanzhou and Wushan section.This indicated that biomagnification power of mercury is greater in tributary than in main stem of TGR.Carbon and nitrogen stable isotope analysis also indicate a difference in food source of fishes between tributary and main stem.In tributary(Shennong River),the values of fish samples were-22.08‰-28.92‰ for δ13C and 8.26‰-13.15‰ for δ15N;In main stem,the values of fish samples were-23.11‰-26.87‰ for δ13C and 8.95‰-16.98‰ for δ15N.This indicate fishes in tributary rely more on pelagic primary production while those in main stem tend to take allochthonous materials carried by runoff.In conclusion,the body type of tributary and main stem after impoundment could be different,and this may be an important reason of different mercury bioaccumulation between tributary and main stem within TGR.

The study was aimed to solve the problem of high level in turbidity, bad smell and taste leading in negative influence on the river landscape, which were caused by the high level of suspended substance, nitrogen and phosphorus in parts of urban rivers where the recycled water was used as water resource. The field test research focused on purifying polluted water in Kun Yu River by the biological contact oxidation process (BCOP) in Beijing. The rate of the flow in the pilot test was designed to 32m3/d, while the hydraulic retention time (HRT) was 5h. The results showed that the test system had good removal efficiency in turbidity which reached to 70.0% of the mean removal rate and the turbidity of effluent is steady during the six months of operation. The results of particle size analysis showed that the system also had high removal efficiency in large-diameter particles in river and the particles larger than 1000 microns were completely removed in the outflow of the channel simulator. Meanwhile, the system of BCOP utilized could effectively reduce the organic matter and nutrients in the channel simulator. The mean removal rate of CODCr, BOD5, Ammonia nitrogen, TN and TP were 61.48%, 69.64%, 71.70%, 30.77%, and 41.79% respectively.

Polycyclic aromatic hydrocarbons(PAHs) of 16 types were measured in sediment from Xidayang Reservoir,Hebei Province,and the possible sources and potential risk assessment also had been analyzed.Total PAHs concentrations varied from 422.36 to 1052.90ng/g in surface sediment,and increased continuously from reservoir upstream to the front areas of the reservoir dam.The total PAHs concentrations ranged from 388.81 to 1205.56ng/g in a sediment profile,and increased continuously from the bottom(20cm under the surface) to the surface sediment.Naphthalene,Phenanthrene,Fluoranthene,Benzo(b)fluoranthene,Chrysene and Pyrene were dominant compounds of PAHs in the sediment.The total PAHs concentration was positively correlated to TOC contents with a correlation coefficient of 0.91 in surface sediment and 0.93 in profile sediment.TOC absorbs more strongly high molecular weight PAHs(HPAHs) than low molecular weight PAHs(LPAHs).The main source of PAHs was originated from combustions of fossil fuels and biomass.In general,PAHs pollution in sediment appeared to be moderate to low leveling in Xidayang Reservoir.Risk assessment suggested that PAHs was no significant biological impairment,suggesting a low toxicological risk up to now.

16 polycyclic aromatic hydrocarbons (PAHs) of sediments were measured in Wangkuai Reservoir, Hebei Province. The results showed that the sediments of Wangkuai Reservoir appear to be moderate pollution by PAHs. PAH pollutions became more serious from reservoir upstream to front of the dam. The total PAHs concentrations decrease with the depth of sediment. Nap, Phe, Fla, BbF, Chr, and Pyr were dominant in sediments. The total PAHs concentration was directly proportional to the content of TOC with a correlation coefficient of 0.8154 in surface sediments and 0.9534 in profile sediments. Combustion of fossil fuels and biomass was the main source of PAHs in sediments of Wangkuai Reservoir. The result of ecological risk assessment indicated that high potential ecological risks of PAHs were not found in sediments of Wangkuai Reservoir, but Flo compound was present in excess of the lower ERL and may exist biological effects.

The rule of removing phosphorus in small-scale simulated wetland system has been studied.Considering the influence of the environmental factors as dissolved oxygen,pH,etc,we chose not only the aquatic plants,but also rooted emergent macrophyte as the experimental macrophytes.By contrasted four kinds of macrophyte systems,we found out that the absorbency and functionary mode of removing phosphorus by macrophytes are different.As a whole,we found out the three stages model of the density dropping of phosphorus,namely:slope lower stage,steep lower stage,steady lower stage,and the removal rate of each stage is:35.53%, 29.98% and 7.20%.

Investigations of the phytoplankton, zooplankton, zoobenthos and aquatic vegetation in Lake Qiluhu were carried out in February, 2009. Over the whole lake, 13 sampling sites were set up for the analysis of phytoplankton and zooplankton, and 22 profiles for the collection of macrophytes and zoobenthos. In the survey, 7 phyla, 65 algae species were identified. The average abundance of phytoplankton was 7.16 × 108 cells/L, and the dominant specie was Limnothrix redekei. No obvious surface accumulation of algae was detected. The concentration of Chlorophyll a ranged from 85 to 101 μg/L, and the average value was 93 μg/L. Nineteen species of zooplankton were observed, including 4 species of rotifers, 6 species of cladocerans and 9 species of copepods. Copepods were the dominant species, their abundance reaching 68%, whilst Cladocerans took second place with an abundance proportion of 28%. Six species of submerged vegetation were identified: Potamogeton Pectinatus, Myriophyllum, Elodea Canadensis, Ceratophyllum demersum and Potamogeton crispus. Amongst them, the dominant vegetation was P. Pectinatus, the biomass of which was up to 63% of the total biomass. Emerged macrophytes were cluster distributed across the whole lake, mainly consisting of Scirpus tabernaemontani, phragmites communis and cane shoots. Unfortunately, no living zoobenthos were found at the sites. The results indicated that, in Lake Qiluhu, the abundance of phytoplankton was maintained at a high level. The ecological function of submerged vegetation was gradually being lost because of its low standing crop and coverage, and the benthic animal habitat was severely damaged.